This invention relates to polymeric adsorbents and ion exchange resins of the macronet type, methods of preparing the adsorbents and resins, and uses of the adsorbents and resins for water-treatment, recovery of organic materials from gaseous and other streams, pharmaceutical purification and processing, catalysis, and similar applications.
Adsorbents are commonly solids which exhibit selectivity at their surface for substances in a mixture, thereby providing a means of separating such substances from the mixture. The high surface area characteristic of adsorbents (usually well above 5 m..sup.2 /g. of solid) normally results from a fine state of subdivision (non-porous adsorbents) or from pores in the adsorbent particles (porous adsorbents). Carbon black and TiO.sub.2 and ZnO pigments are examples of non-porous adsorbents. Granular carbon, silica gel, bone char, certain soils and asbestos are examples of well-known porous adsorbents obtained from naturally occurring materials. For separation or purification of complex substances (such as pharmaceuticals) synthetic adsorbents have been developed, some of which serve also as ion exchange materials or as intermediates for the manufacture of ion exchange materials. However, ion exchange is an absorption as well as an adsorption phenomenon, so that although all ion exchange materials are adsorbents, the converse is not necessarily true.
The synthetic adsorbents generally are porous polymeric solids, polystyrene and styrene-divinylbenzene copolymers being representative. Although it is possible to prepare synthetic polymers in a fine state of subdivision, or to grind such polymers to a fine particle size, to obtain high surface area, fine particle size adsorbents cannot be used in cyclic processes, particularly processes involving columns, since the fine particles pack too tightly and impede flow. Adsorbents of moderately large particle size, of the order of about 0.02 mm. to 2 mm. diameter or greater, are therefore required. Polymeric beads, obtained by known suspension polymerization techniques, have a convenient particle size for use in columnar operations. Nevertheless, although the polymeric adsorbents can be made hydrophobic and the bead form enhances the usefulness of the polymeric adsorbents, their adsorbent properties have been too limited to enable the adsorbents to compete effectively with the carbonaceous adsorbents obtained from the pyrolysis of organic materials. However, the latter suffer from high moisture pickup in humid atmospheres, have poor reproducibility during manufacture, and have such fine pores and rigid structure as to crack, split and decrepitate under the high osmotic pressures commonly encountered in cyclic operations.
An object of the invention is to provide synthetic polymeric adsorbents and ion exchange resins which combine the best properties of known synthetic polymeric adsorbents and carbonaceous adsorbents but without the most serious deficiencies of either class. Accordingly, the adsorbents and ion exchange resins of the invention have moderate and uniform particle size (to permit use in columnar operations), are hydrophobic, have good physical stability (resistance to cracking and other forms of destruction under osmotic pressure), have high surface area and/or high porosity, and sometimes exhibit high adsorption capacity without exceptionally high surface area and/or porosity. In this regard, even though certain of the adsorbents lack the extremely high surface areas of known polymeric adsorbents or activated carbon adsorbents, they equal the performance, or even outperform, such adsorbents, especially in their adsorption capacity for organic liquids at high concentration.